Preliminary Study on the Fate of VX in Concrete

Abstract

A preliminary study has been done to examine the sorption and reaction of VX, O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate, in an aged sample of concrete using 31P NMR. Using “solution” NMR conditions, facile sorption of a neat liquid 15 μL droplet of VX into a 737 mg chunk of the concrete could be observed. The half-life for this process is about 2 min and is attributed to VX penetrating the surface pores to form a sorbed phase tentatively assigned to a solid protonated form of VX. Little reaction occurs during this initial sorption period; however, the sorbed VX does slowly hydrolyze with a half-life of about 3 months. During this time, the hydrolysis products of VX, ethyl methylphosphonic acid (EMPA), and diisopropylaminoethanethiol (DESH), but not VX itself, are observed to condense on the inside of the NMR tube around the concrete chunk. Using “solid state” MAS NMR conditions, examination of the reaction of a 5 μL VX drop with 293 mg of the crushed concrete revealed a two-step behavior in the kinetics. An initial reaction with a half-life of about 2 h consumes 12% of the VX. After about 1 h, a much slower steady-state hydrolysis ensues, exhibiting a half-life of 28 days. EMPA is the sole hydrolysis product detected in the 31P MAS NMR spectra; no toxic S-[2-(diisopropylamino)ethyl]methylphosphonothioate (EA-2192) is observed. Considering the concrete surface area, one monolayer would accommodate 13% of the applied VX. Thus, the observed kinetic behavior is consistent with the concrete surface possessing a limited reactive capacity corresponding to about one VX monolayer.